Oxidation and coloration of ferrous surfaces



UNITED STATES PATENT OFFICE.

LIMITED, OF LONDON, ENGLAND.

OXIDATION AND GOLORATION OF FERROUS SURFACES.

No Drawing.

To all whom it may concern:

Be it known that we, TITO RONDELLI and QUIRINo SEsTINI, subjects of the King of Italy, residing at Turin, Italy, and Bergamo, Italy, respectively, have invented certain new and useful Improvements in Oxidation and Coloration of Ferrous Surfaces, of which the following is a specification.

This invention relates to the oxidation and coloration of ferrous surfaces, and has for its object to provide an improved process for this purpose.

In the prior British specification, N 0. 106,774 (No. 16582 of 1916) a process for bronzing or coloring ferrous surfaces is described, according to which the surface to be bronzed or colored is electrolytically coated with iron from an electrolyte which is a hot dense alkaline solution (for example, having a temperature of about 120- 140 C. and a density about 1.3-1.5) containing an oxid of iron combined with or in solution in the alkali (for example, containing a ferrite) and the surface is then colored or bronzed for example, by anodic oxidation in the electrolytic bath, or by immersion in an alkaline oxidizing solution, such as a solution of caustic alkali containing a metallic nitrate, or an aromatic nitro-derivative such as nitro-phenol. It has now been found that ferrous surfaces may be oxidized and colored with excellent and varied effect by a modification of this process.

According to the present invention, the improved process for the oxidation and coloration of ferrous surfaces, that is to say, of iron or steel surfaces, comprises submitting the surface to anodic oxidation only in a hot concentrated alkaline bath, for example, a concentrated solution of caustic soda. The concentration of the bath and the temperature may vary within certain limits, but preferably, the concentration 1s such that the bath-boils between about 135- 180 0.

Organic or inorganic oxidizing agents may be added to the bath as desired and as suitable agents of the kind may be men tioned alkali nitrates and chlorates. For example, from 10-20 per cent. of sodium nitrate may be added to the bath.

The current density may vary within wide limits, the particular density employed depending upon the effect desired, the nature Specification of Letters Patent.

Application filed August 24, 1920. Serial No.

Patented Aug. 2, 1921. 405,599.

of the surface under treatment, etc. As a guide it may be said that for a steel of ordinary hardness a current density of about 10-15 amperes per square decimeter will frequently be found suitable.

The following examples will serve to in dlcate how the process may be carried into effect, but it is to be understood that they are illustrative only and that the invention is not limited in respect to the details set forth.

Example I.

A solution of caustic soda is prepared, of such concent ation that it boils at about 160 C. This solution is brought to a temperature of l45-155 C. and the object to be colored is immersed and made to serve as anode, while a current of 10 amperes per square de'cimeter is passed through. the solution. The surface becomes colored a violet-blue. This takes place within a few seconds if the object be small; for larger obects a correspondingly longer period of treatment is required, that is until the ob- ]ect has reached the temperature of the bath.

Ewample- H.

A solution of caustic soda which boils at about 170 is made up. A steel object is submitted to anodic oxidation in this solution, under a current density of from 10-15 amperes, the temperature being about 160- 165", until a bronze coloration is obtained, the precise time required for this effect to be produced depending upon the size of the object for the reason stated in the preceding example.

The particular effect obtained depends upon the conditions of working, such as the composition of the bath, period of immersion, the current densit and to a lesser degree upon the nature of the surface under treatment, but in any given case a simple preliminary experiment suffices to determine the factors necessary to attain the desired result. In every case time must be allowed for the object to attain the temperature of the bath. The current may be passed while the object is being heated up by thebath or after the object has reached the required temperature.

Frequently an improved effect may be obtained by immersing the article, after removal from the bath and drying, in hot oil,

for example, in olive oil, or in a mixture of linseed and mineral oil heated to a temperature of about 150-180 C.

What we claim as our invention and desire to secure by Letters Patent is 1. The process for oxidizing ferrous surfaces which consists in submitting-the surface exclusively to anodic oxidation in a hot concentrated alkaline electrolyte containing an oxidizing agent.

2. The process for oxidizing ferrous surfaces which consists in submitting the surface exclusively to anodi'c oxidation in a hot concentrated alkaline electrolyte containing an alkali nitrate.

3. The process for oxidizing ferrous surfaces which consists in submitting the surface exclusively to anodic oxidation in a hot concentrated alkaline electrolyte and subsequently immersing the object, the surface of which has been oxidized in hot oil.

4. The herein described process for oxidizing a ferrous surface which comprises immersing the surface in a solution of alkali of such concentration as to boil at a temperature of at least 135 C and submitting the surface to direct anodic oxidation at a temperature above 130 C.

5. The herein described process for oxidizing a ferrous surface which comprises immersing the surface in a solution of caustic alkali of such concentration as to'boil at a temperature of at least 135 C. and submitting the surface to direct anodic oxidation at a temperature above 130 C.

6. The herein described process for oxidizing a ferrous surface which comprises immersing the surface in a solution of caustic alkali of such concentration as to boil at a temperature of at least 135 C. and submitting the surface to direct anodic oxidation at a temperature above 130 C. under a current density of 10-15 amperes per square decimeter of the surface.

7. The herein described process for oxidizing a ferrous surface which comprises immersing the surface in a solution of caustic alkali of such concentration as to boil at a temperature between 16017 0 C. and submitting the surface to direct anodic oxidation at a temperature of 145-155 C.

In testimony whereof we have signed our names to this specification in the presence of two subscribing witnesses.

TITO RONDELLI. QUIRINO SESTINI. 

